During the two wintering seasons from 2004 to 2005 and 2006 to 2007, the habitat use of hunting Eastern Marsh Harriers Circus spilonotos was studied at four sites in the Watarase Marsh of central Japan. During both seasons surveyed, the frequency of hunting flights was significantly higher in an artificial reedbed (Site A) with ditches, small ponds and lakes, than in a dry reedbed (Site B). Site A had a significantly greater number of bird species and a larger population of the harriers' potential prey than Site B. For the purpose of analysis, the survey sites were completely divided into a grid with a cell size of 100m by 100m. Cells with ditches and/or ponds had a significantly greater number of hunting flights than those with only tall vegetation. These results suggest that reedbeds with ditches and ponds provide abundant prey for the harrier and also may facilitate the surprise hunting technique in which the harrier is specialized. The conservation or creation of reedbeds with a diverse structure is assumed to be beneficial to the conservation of wintering Eastern Marsh Harriers.
2008 by Japan Bird Research Association